The present invention relates to an apparatus for photometrically testing several specimens (12) that are each irradiated by an associated light source. An apparatus of this type is used to photometrically test several specimens, for instance on-line on a thermocycler, in order to monitor the progress of PCR procedures. However, such an apparatus is also used to test a plurality of microarray spots on glass slides, or as well wherever a plurality of specimens must be tested photometrically by means of fluorescence, absorption, scattering phenomena, and the like. When testing fluorescence specimens, an appropriate fluorescence indicator is added as a rule.
Such an apparatus, however, incurs the drawback of entailing a plurality of light paths, which, in turn, require a complex design. When only one light path is used between a light source and a light sensor, then the specimens must be moved sequentially into the light path and substantial mechanisms are entailed. It is furthermore known to move the light, such as a reflected light, over stationary specimens. Unfortunately, this design incurs the same drawbacks as above.
On the other hand, to simultaneously irradiate all specimens simultaneously by the same light source and to view them individually using several sensors would be exceedingly costly. This is due, in part, to the fact that the sensors are much more expensive than light sources.
Accordingly, the patent documents EP 0902271 A2 and WO 01/35079 A1 propose individually irradiating the specimens using associated light sources and to use only one light sensor to determine and analyze the light from all specimens, namely the summed signal.
This solution, however, raises the problem of identifying the light intensities of the particular specimens from the summed signal picked up by the sensor. The state of the art disclosed by both of the above patent documents solves this problem in that the different light sources are operative only individually, so that only the light from a given specimens will fall on the sensor which only receives a single specimen's light that, provided there be appropriate synchronization, can be allocated to the particular specimen.
However such apparatus suffers from drawbacks because, assuming there are n specimens, each specimen may be illuminated at most only 1/n of the available measuring time. The values related to the particular specimens are available only within short time intervals. Moreover, the measured signal cannot be integrated over a substantial length of time, illustratively when the signal is weak, to still attain in this manner a good signal to noise ratio. If the signal fluctuates, or when ascertaining the progress of a reaction in the specimens, it will be impossible to monitor the signal as a function of time.